The present invention relates to jewelry stones in general, and more particularly to brilliant-cut jewelry stones. It also relates to a method of cutting such stones.
Brilliants are gem stones, usually diamonds, European cut or the American cut, providing them with facets. The term brilliant which is given to gem stones cut in this manner refers to the fact that because of the special type of cut given them, they have a particularly brilliant and sparkling appearance. Generally speaking, a brilliant has a girdle, meaning the circumferential zone at which the upper portion of the stone, called the bezel, and the lower portion which is called the pavilion, join one another. Reference to upper and lower portions is clearly understood here, because the bezel has, in a plane which usually parallels the general plane of the girdle, a surface called the table which in the normal viewing position faces upwardly.
Brilliants of the cuts known heretofore have their facets which are provided on the pavilion, inclined with reference to the general plane of the girdle at angles of between 38.7.degree. up to 40.9.degree.. The upper facets, that is those provided on the bezel, are inclined to the general plane of the girdle at angles of between 25.5.degree. up to 41.1.degree.. The respective pair of angles meets the equation established in 1926 by A. Johnson, which gives for the particular material via the refraction index (n) those angles for the upper and lower facets which will afford the maximum possible reflection.
The invention disclosed in my copending application provides a substantial improvement over what has heretofore been accepted in this art. However, I have since found that I can provide such improvements not only in gem stones, i.e., precious stones, but also in other transparent materials which are used for costume jewelry and the like, for instance paste.
Therefore, the present invention relates also to transparent jewels made of natural and synthetic substances. Therein are determined the facet angles of the brilliant cut within narrow limits and deviating from the known commercial cuts to better utilize the rough stone on the one hand to preserve the brilliance of the brilliant on the other hand. Among the transparent materials diamond is the most valuable substance for which it is especially rewarding to preserve the material of the rough stone in the brilliant. Since in the commercial diamond brilliant cut quite specific proportions must be maintained and some rough diamonds are considerably different from the classical octahedral shape, it is required to cut away up to 67% of the valuable substance when the finished cut stone is to exhibit brilliance.
The brilliant cut is of characteristic shape. Initially square in its basic shape, it has developed in the course of two centuries to a round shape as full-cut brilliant with a predetermined number of facets and with quite specific facet angles. Above the girdle are disposed the crown or bezel facets at the facet angles, and these facets are delimited by a table which is parallel to the girdle. The height of the upper portion of the diameter of the table with respect to the girdle are determined within very narrow limits if the brilliant is to exhibit a convincing brilliance. The facet angles of the rear portion below the girdle are in commercial cuts in still narrower limits than the above cited bezel facet angles. This type of cut is supposed to achieve the optical optical object of reflecting all light that is incident upon the brilliant at the pavilion facets thereof, in order to emit this light through the table and the bezel facets toward the viewer. A large number of such reflections shall impress the viewer. The light which is emitted rearwardly through the pavilion facets reduces the number of reflections.